In a catalytic heater, heat is produced when a gaseous fuel is brought into contact with a catalyst in the presence of air containing a normal level of oxygen. Typically, the fuels are natural gas, propane and butane, for example.
Generally, the combustible gas or fuel is fed through the bottom of the catalytic heater and is dispersed at atmospheric pressure into contact with a porous active layer. This layer contains the catalyst which may be platinum, for example. Oxygen from the atmosphere enters the porous catalytic layer and reacts with the gaseous fuel, promoted by the catalyst. This reaction releases the BTU content in the fuel in the form of radiant energy. Catalytic heaters are therefore used as a source for infrared heat. The chemical reaction that occurs during the oxidation reduction process produces temperatures within the catalyst of from about 500 to 1000 degrees Fahrenheit (F). The actual temperature at the surface of catalytic heater is dependent upon the rate at which the fuel gas is introduced to the catalyst. The surface of the heater is typically rectangular or circular and ranges from about one square foot to about 10 square feet. The volume of the gas delivered to the catalytic surface may range from about 2 to 6 cubic feet of gas per hour per square foot.
Before a catalytic heater can be operated successfully, the heater and more particularly the catalyst must be preheated to a temperature at which the oxidation reaction can be sustained. At the present, most all catalytic heaters use an electric resistance tubular heater (calrod) to preheat the platinum catalyst before the gas is introduced into the heater. However, some manufactures of catalytic heaters are attempting to use methods of preheating the catalyst other than with an electrical element. These methods include a flame pilot light that impinges the internal or external surface of the catalyst, raising its temperature high enough for the catalyst to flamelessly oxidize the incoming gas fuel. Another method consists of ducting hot air in close proximity to the catalyst, raising the temperature sufficiently to react the incoming gas fuel.